Various types of hearing aids are known which have non-directional or omni-directional response characteristics; and, other types of hearing aids are known which have directional response characteristics. Still other prior art hearing aids are known which can be utilized either as directional hearing aids or as omni-directional hearing aids by suitable modification of the structure. However, such other prior art hearing aids, which can be used either as directional or omni-directional devices, have the marked disadvantage that when the aid is used as a omni-directional aid, it will have a given response characteristic relative to frequency, and when the aid is used as a directional aid, it will have an entirely different response characteristic relative to frequency. For example, curve or response line A of FIG. 3 in prior art U.S. Pat. No. 3,835,263 (Killion) shows a typical response of an omni-directional device wherein the lower frequency portion of the curve is relatively flat and then drops off at the higher frequencies. Curve B in FIG. 3 of the prior art Killion reference shows the frequency response characteristics of a directional device wherein the frequency response rises from a low value as a relatively straight line to a maximum level and then drops off at the higher frequencies.
Accordingly, it was an object of the prior art Killion reference to provide a microphone assembly particularly for use with hearing aids, which assembly can be operated either in a directional or a omni-directional mode, but which has essentially the same response characteristics relative to the frequency for sound arriving from the preferred direction whether it is operated in a directional or omni-directional mode.
The prior art Killion reference, however, did not provide flexibility in independently choosing the resulting frequency response of the microphone in the directional and omni-directional modes. In addition, the prior art Killion reference was acoustically complex and consequently difficult to implement.
It is therefore an object of the present invention to provide a less acoustically complex assembly having the same frequency response in the omni-directional and directional modes of operation, while also allowing flexibility in adjusting the frequency response of the microphone in the directional mode.
Other objects of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.